Ancient natural global warming

Scientists are unravelling the environmental changes that took place around the Arctic during an exceptional episode of ancient global warming. Newly published results from a high-resolution study of sediments collected on Spitsbergen represent a significant contribution to this endeavour. The study was led by Dr Ian Harding and Prof John Marshall of the University of Southampton’s School of Ocean and Earth Science (SOES), based at the National Oceanography Centre, Southampton.

Around 56 million years ago there was a period of global warming called the Paleocene–Eocene Thermal Maximum (PETM), during which global sea surface temperatures increased by approximately 5°C.

The warming of the oceans led to profound ecological changes, including the widespread extinction of many types of foraminifera, tiny single-celled organisms with distinctive shells. Plankton that had previously only prospered in tropical and subtropical waters migrated to higher latitudes. Similar changes occurred on the land, with many animals and plants extending their distributions towards the poles.

“Although environmental changes associated with the PETM at low- to mid-latitude settings and high southern latitudes are well documented, we know less about these changes at high northern latitudes,” explained Dr Harding.

Information about the Arctic environment during the PETM has come predominantly from sediment cores drilled from under the pack ice on the Lomonosov Ridge (~ 88°N) by the Integrated Ocean Drilling Program (IODP Site 302-4A). However, these cores do not span the entire PETM and therefore do not provide a complete picture.

“Information from other Arctic sites is needed for a better understanding of PETM environmental conditions, such data can then in turn be used in computer models which will improve our understanding not only of past climatic conditions but also enhance our ability to predict future perturbations,” said Dr Harding.

To help fill this knowledge gap, Dr Harding’s team turned to a site (~78 °N) on Spitsbergen in the high Arctic. Here, 2.5-kilometre-thick sediments span the critical period. During the PETM, the site would have been at around 75 °N, the difference in position being due to the slow movement of tectonic plates over millions of years.

Through analyses of plankton and the chemical and magnetic characteristics of the sediments, they were unambiguously able to identify a 15-metre succession of exposed sediment representing the approximately 170 thousand year PETM event.

At the base of the segment they found the preserved remains of the cyst-forming dinoflagellate Apectodinium augustum, a planktonic species diagnostic of the PETM across the globe. In fact, the species was already present in Spitsbergen before the shift in carbon isotope composition formally marking the onset of the PETM, suggesting that environment change was by then already well underway.

Fieldwork in Spitsbergen

Along with data from other sites, their Arctic evidence suggests not only that sea level began to rise well before the formal onset of the PETM, but also that it peaked about 13,000 years into the period. At the same time, increased surface-water run-off from the land dampened water-column mixing and led to stratification, with an upper freshened layer that overlay denser, more saline seawater beneath.

By carefully comparing their results with those from IODP Site 302-4A to the north, they found evidence for regional differences in the environmental manifestations of the PETM in high northern latitudes. For example, the evidence from the IODP site suggests that the sunlit surface layer of the ocean was often depleted of oxygen, the results from Spitsbergen suggest that oxygen depletion was largely restricted to the bottom waters and sediments. In addition, they found that pollen from flowering plants was scarce, unlike at the IODP site, suggesting that conditions around the Spitsbergen Central Basin may not have been conducive to the growth of flowering plants during the PETM.

“Because this geologically short-lived event is represented by such an expanded section at Spitsbergen by comparison to other deep water sites, this locality has provided us with opportunities for further high-resolution studies of the PETM, which we are currently preparing for publication,” concluded Dr Harding.

Preliminary field work was funded by The Millennium Atlas Company Limited, and a second expedition with other members of the palaeo-Arctic Climates and Environments (pACE) group was funded by the Worldwide Universities Network.

48 thoughts on “Ancient natural global warming”

A couple of years ago I drove from Calgary to Inuvik, a journey that included 700 km of the dirt road called The Dempster. We travelled through two mountain ranges in the Yukon and down to the southern end of the Mackenzie delta, where the road travelled along ridges to stay out of the muskeg swamps and permafrost muds. We flew to Banks Island where we trundled around in quads seeking muskoxen and cariboo. Unfortunately for warmists, I am a geologist with a multi-decadal interest in glacial and post-glacial events, for what I saw was not wat they wanted to hear about. (Another trip to Churchill where the polar bears, not antelope roams, has a similar, non-saluatory result in discussions with warmists.)

The Mackenzie delta is 150 miles or so long because the land is rising and the shoreline is what they call “regressive”. The shoreline deposits of Banks Island are about 25m higher than they were about 12,000 years ago when the main glacial masses melted. The thermokarst lakes near the shoreline exist because, finally, the warmth of the post-glacial times has melted blocks of ice or frozen ground beneath the surface – not because the air has more CO2 in it. Near Eagle Plains the university geologists are studying a 700,00 year-old perafrost layer uncovered by a landslide. The Arctic is not subject to sudden, significant changes. The land continues to rise.

At Hudson Bay the land continues to rise at about 4 cm/year. If you want to find Inuit camps 4000 years old, you have to go 100km inland. Lake Winnepegosis continues to get bigger because the spillpoint between the Lake and Hudson Bay is still rising.

Sure the Arctic ice is smaller in summer than it was in the 70’s. There were huge malaria outbreaks in the North up to the 40’s. Things change. Without us. Get a grip: it isn’t all us. And the Arctic will not become flooded in our grandchildrens lifetime with even severe changes. Of which there is no long-term indication.

If we went back to the Garden of Eden, the North would be underwater and the Inuit would be periodically starved to death. The great ancestors to the Inuit – themselves interlopers from the west when the Arctic waters opened about 5000 years ago and enabled them to “invade” the country – died out as a result of social collapse of small communities stressed out by a terrible climate.

Huge changes have occurred in the Arctic, and it survives well. And we didn’t cause them. What are the results up there that look any different from what has happened over the last few thousand years, and what are we doing that will make things “worse”? Polar bears moving north? Cariboo herds increasing as plant growth increases? Inuit living in the winter at -30C instead of -35C? In the summer it has always been hot, as my field work in the mid-70s (during Global Cooling) revealed to me.

The Arctic is said to be the “canary in the coal mine” of CAGW. From what I have experienced, the canary is just fine.

The St. Lawrence estuary “suddenly – in geological terms” dumping an entire freshwater inland sea into the north Atlantic currents when a glacier retreated enough to allow water to flow north? ( Or same as an outflow out of the Hudson with the St/ L. blocked by ice)

The boundary layer that marked the end of the dinosaurs is well known, for example, as a layer worldwide.
I could get behind a significant increase in Atmospheric pressure, a la outgassing, as a cause of PETM. In that case, it wouldn’t matter what the ratios of gases were as long as there was significantly more atmosphere.
What other causes have been postulated/supported/searched out?

Situation then and now is not directly comparable. Most of the Icelandic shelf has risen up during the last 50 million years, consequently the Arctic Ocean was more opened to the Atlantic warm currents than it is today.

Jean Parisot: I think you have that backwards…The ice core record generally shows warming events happening faster than cooling. (Perhaps you are looking at graphs that put the present time on the left side of the scale and have the increasing horizontal axis represent going increasingly further back in time?)

I presume that the reason for this is that ice generally can only build up slowly but it can it can disappear more quickly because the dynamics of this involves not just melting but also breaking up.

“Situation then and now is not directly comparable. Most of the Icelandic shelf has risen up during the last 50 million years, consequently the Arctic Ocean was more opened to the Atlantic warm currents than it is today.”

More the other way around, the seaway to the North Atlantic was just opening up at the time.

Rapid oxidation of organic deposits in and around an uplifted former epicontinental sea.

Impact of a volatile-rich comet.

Large scale melting of permafrost in Antarctica.

Unfortunately none of these mechanisms seems capable of liberating enough greenhouse gases to explain the warming.
The mention of Apectodinium showing up before the carbon isotope shift is interesting. This is a feature that have been noted in other areas, and it repeats a familiar pattern: the warming comes first, and a bit later CO2 starts increasing.

Axel Heiberg Island, in the Canadian high arctic, has mummified trees & the remains of a tropical swamp. These have been shown to have grown at this latitude & experienced the months of light & darkness. Also I was under the impression that Spitzbergen started life much further south. Try geodetic forest, Axel Heiberg in Google.

Another candidate for the cause of the PETM is an asteroid or comet impact along the Atlantic seaboard of North America. In particular, there are three or more major impact craters buried in the sediments of the Continental shelf and coastal areas. One of these impact craters is located at the mouth of Chesapeake Bay and is responsible for the deformation of its coastal aquifer.

vukcevic says:
“…Most of the Icelandic shelf has risen up during the last 50 million years, consequently the Arctic Ocean was more opened to the Atlantic warm currents than it is today.” Actually,the Arctic Ocean opened up to warm Atlantic currents only a little over a century ago. This is the cause of present Arctic warming, not some imaginary greenhouse effect. Read “What Warming?”

“SWAG”
———–
I thought it was an acronym and I came up with several suitable rude words for S, W and A but got stuck on G – so I reached for Wiki and found this:

“Swag may refer to:

Swag (album), a 2002 rock album
Swag (bedroll), an Australian waterproof bedroll
Swag (motif), an architectural element
Swag (novel), a 1976 crime novel
“Swag” (Ugly Betty episode), the eleventh episode of the television series Ugly Betty
Swag, a type of window valance, often in combination with a full curtain underneath
Swag, promotional items given away at trade fairs and events to encourage attendees to visit the vendors’ booths”

Wonder what pulled the planet from a greenhouse state to the current icehouse conditions? The azolla fern. A fantastic fairytale of the superplant that we have to thank for ice-covered poles. Enjoy:http://en.wikipedia.org/wiki/Azolla_event

Brownedoff says:
February 27, 2011 at 3:10 pm
““SWAG”
———–
I thought it was an acronym and I came up with several suitable rude words for S, W and A but got stuck on G – so I reached for Wiki and found this:”

There has been a lot of scientific debate going on about the effects the Chesapeake Bay impact/s had upon the global climate and atmospheric-oceanic chemistries versus the Deccan Traps vulcanism. I have often wondered and speculated whether or not they are missing the possibility that the Deccan Traps vulcanism could have been brought about by a series of these major impact events. When the Shoemaker-Levy comet impacted Jupiter, we could see first-hand how the Jovian gravity caused the comet to break into pieces and impact across widely spaced trails across Jupiter. Similar impact events on a far smaller scale may have been detected as trails of impact craters acorss the Midwest of the United States. The Chesapeake crater it appears may have been accompanied by other major imapct craters farther north. There are one or more major impact craters off the coast of India which may have a connection to the vulcanism of the Deccan Traps. I can’t help but wonder if perhaps one or more major impacts at this time were of sufficient energy to disrupt the crust and upper mantle to cause some extreme vulcanism evnts in the Deccan Traps and elsewhere, thereby causing some major changes in climate? The role of such speculated major changes in climate due to impact events versus the PETM is another question.

The PETM spans nearly two Ice Ages cycles in length.
What caused this?
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Greenhouse gases – perhaps related to volcanism, perhaps with a contribution from methane clathrates
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There has never been a time that I have heard about when when CO2 increased BEFORE temperatures rose. Please cite references.

At 50 million years even the 800 year lag reported between warming and CO2 might be undetectable.

Please stop trying to come up with a local, geological source of extra CO2 to explain the PETM. Get it through your heads – – CO2 ain’t important and, if anything, it is an effect of global climate change, not a cause.

The most likely explanations of the PETM temperature increase is one or two things. More shallow epeiric seas (Tethys) then were able to store and distribute more solar-induced heat energy. Second, the sun may have been more active then, either in the form of increased irradiation or more effective transmission of solar output to the oceans (reduced cloud cover).

Drives me nuts when folks go looking for changes in a trace gas to explain major climate changes. Big change needs a Big Cause, and that fundamentally means the Sun.

Jim Cole says:
February 27, 2011 at 6:02 pm
Please stop trying to come up with a local, geological source of extra CO2 to explain the PETM.

Atmospheric carbon dioxide concentrations were on a major downtrend from 2,000ppm to less than 1,000ppm, except for a brief and minor blip of about 50-100ppm resurgence in the early Tertiary. So, don’t think discussion of the PETM necessarily involves an assumption that a warmer or colder climate at the time of the PETM was supposed to be caused by CO2. The global temperatures were stable and far higher than present while the carbon dioxide levels more than halved at the time.

There are two rather curious statements in the article. The first is in regard to plankton indicative of the PETM:

And another regarding sea level rise:

Does it not strike anyone else as odd that the effects of the PETM seem to have started appearing before the PETM is thought to have begun? How can one sort out cause and effect when the supposed effects are appearing before the PETM begins, implying that what ever caused those effects happened even earlier? Either those effects, and their cause, have nothing to do with the PETM, or else the PETM itself is just a delayed effect of the same cause.

One could resolve the matter I suppose by advancing the date of the official start of the PETM to an earlier time that encompasses the increase in plankton and sea level rise, but leaves another obvious canundrum unresolved. My understanding being that the “official” start of the PETM is a shift in carbon isotopes indicating a sharp rise in temperature. Is it not odd that the plankton which require higher temperatures to thrive, and the sea level increase which would require higher temperatures to occur, both happened before the increase in temperatures is thought to have begun?

By that logic, we need not worry about warmer temperatures melting the ice caps and raising the sea level. We need to worry about the sea level rising and causing a temperature increase.

My first crack at HTML not so good. The two statements I was trying to reference in my previous comment were:

the species was already present in Spitsbergen before the shift in carbon isotope composition formally marking the onset of the PETM, suggesting that environment change was by then already well underway.

and

Along with data from other sites, their Arctic evidence suggests not only that sea level began to rise well before the formal onset of the PETM

netdr2 says:
February 27, 2011 at 4:04 pm
___________________________
For the PETM data in Figure 5 of Zachos, et al., in Science 292 (27 April 2001, page 690), if you equalize the amplitudes of d18O (inverse proxy for benthic temperature) and d13C (benthic carbon), there is insufficient resolution of lead-lag during the temperature/carbon rise, but temperature falls many thousands of years before carbon after the peak. Once again, phase indicates that carbon cannot have controlled temperature, but temperature plausibly controlled carbon though its effect on clathrate volume.
Even for those who believe in a para-normal temperature that somehow senses future levels of carbon, it must be a test of faith to observe that there was no runaway greenhouse effect after the PETM. Perhaps that is why the believers are so shrill about the possibility of one now, at much lower levels of temperature and carbon.

Not mentioned are any galactic effects/calamities such as nearby supernova/nova or other stellar outbursts as the Solar System travels about it’s orbit. The Sun is also suspect, along with the usual comet/asteroid impacts. Toss in a close-passing star. The PETM may have been a one-time event never to be repeated.

If they can’t figure out WHAT caused the warming the information can only be speculated about and should not be used in any way to predict the future, or any damned CO2 models. All it shows is there was climate change with no human intervention.

If PETM was such a rare one-a-hundred-million-years event, it would be plain foolish to think it was caused by such an ubiquitous mundane thing as clathrate or volcanic trapps outgassing, or asteroid impact – as these things happen much more often than once a blue moon.

BTW, what happened at tropical latitudes during petm? Did they freeze, or stayed the same, or steamed?

Along with data from other sites, their Arctic evidence suggests not only that sea level began to rise well before the formal onset of the PETM, but also that it peaked about 13,000 years into the period. At the same time, increased surface-water run-off from the land dampened water-column mixing and led to stratification, with an upper freshened layer that overlay denser, more saline seawater beneath.

A sea level rise peak after about 13000 years is interesting – this is about the duration of interglacials. Perhaps it points to some self-limiting oceanic cycle of warming and sea level rise, and could point to why the interglacials are limited to this duration. Certainly from the perspective of the Holocene our own sea level rise is asymptotically slowing.

Some comments here question the order of cause and effect. In this regard, oceanic stratification may not only be an effect of warming – it can be its cause, and the converse also – increased vertical mixing by itself, of a generally highly thermally stratified ocean, is a sufficient cause of climate cooling.

Another interesting observation – no CO2 epilogue to the paper! Perhaps the work of Willis and others in criticizing ill-thought-out political mantras on CAGW tagged onto journal climate related publications is giving authors pause for thought – never a bad thing.

No relation I am afraid!
At least the U. of Southampton is doing proper research. Their last output ‘proved’ that extra CO2 caused acidification of sea water. They put hydrochloric acid into the water to dissolve sea shells. This was their proof of acidification.
We might now get the correct answers to the question about past climates.

If PETM was such a rare one-a-hundred-million-years event, it would be plain foolish to think it was caused by such an ubiquitous mundane thing as clathrate or volcanic trapps outgassing, or asteroid impact – as these things happen much more often than once a blue moon.

Not quite that rare. There was two similar though milder events a few million years later in the Eocene and a very similar episode in the Toarcian (Early Jurassic, c. 180 million years ago).

BTW, what happened at tropical latitudes during petm? Did they freeze, or stayed the same, or steamed?

The two unequivical features of the PETM are the rise in temperature and the rise in CO2.
Whatever the initial cause, one or the other or some other trigger, it is beyond doubt that these two factors reinforced each other with warming generating increased CO2, (possibily via Methane clatherates) and CO2 generating warming.

Not in a runaway feedback of course because the relationship of emissions to temperature raised to the fourth power means that any warming from a GHG effect increases the rate of heat loss at a greater rate so constraining the total warming that it can generate.

For those fascinated with everything Arctic try Barry Lopez’s “Arctic Dreams” an award winning book, chock full of what the title suggests without the doom and gloom of today’s mandatory salute to “climate change,” though, probably not because Mr. Lopez saw through all that but the book was written before climate change became a religion to the left; his later writings suggest a little kool aid intake.

Is it possible we have been seeking answers to variable warming and cooling in the wrong place? No periodic causal effect advanced seems to explain them, save one. A Sun which is aperiodic variable star. Now all we have to do is explain how that works.

I was surfing on the internet the other day, and I’ve also found a mention of a great 3D documentary project about Johnny May, the Inuit aviator, on a website called touscoprod. He has been flying over the arctic area for almost 40 years, and so witnessed the environmental change. .

This documentary project is quite new obviously, and you can become co-producer of the documentary and eventually be rewarded with some exclusive access to great contents and services (meeting with the director, previews, premiere tickets…). I’m in!

D. Patterson says:
February 28, 2011 at 7:15 pm
“Global climate warming is a natural fact in every interglacial period.”

No, global COOLING is a natural fact in every interglacial episode.
The usual pattern is a rapid warming that ends the ice-age within a couple of thousand years followed by slow cooling for anothe 20-40 thousand years.
Temperatures equal to or4 higher than the post-glacial peak 10,000 years after that peak are the exception not the rule.

No, global COOLING is a natural fact in every interglacial episode.
The usual pattern is a rapid warming that ends the ice-age within a couple of thousand years followed by slow cooling for anothe 20-40 thousand years.
Temperatures equal to or4 higher than the post-glacial peak 10,000 years after that peak are the exception not the rule.

That’s funny. I’ll have to post that one, “global COOLING is a natural fact in every interglacial episode,” up on the wall right next to Al Gore’s Snowmageddon and global cooling are caused by [Anthropogenic] Global Warming/Climate Change.

D. Patterson says:
March 1, 2011 at 5:23 am
“That’s funny. I’ll have to post that one, “global COOLING is a natural fact in every interglacial episode,” up on the wall right next to Al Gore’s Snowmageddon and global cooling are caused by [Anthropogenic] Global Warming/Climate Change.”

Perhaps you could post the graph at this link with it to show the measured and consistant pattern of temperature change during the ice-ages.
RAPID warming to a peak and then slow cooling into the next glacial period.

izen says:
March 1, 2011 at 8:05 am
D. Patterson says:
Perhaps you could post the graph at this link with it to show the measured and consistant pattern of temperature change during the ice-ages.
RAPID warming to a peak and then slow cooling into the next glacial period.

During the Eemian Interglacial Optimum the temperatures were comparable to higher than present day. After the peak temperatures were reached, the middle Eemian experienced a cold and dry perod ~122kya, and the temperatures then increased once more to about the present day levels at the end of the Eemian Interglacial. So, past experience demonstrates it cannot be expected that interglacials must always or even typically result in “RAPID warming to a peak and then slow cooling into the next glacial period.”

Furthermore, your implication that the present interglacial is unprecedeented by having a temperature rise to present levels after the early Holocene Optimum is unprecedeented and therefore due to anthropogenic influence is factually incorrect and absurd. It is factually incorrect, because the Eemian Interglacial for at least one of many potential examples had more than one peak tempeerature comparable and/or greater than present. It is absurd to blame the present temperature peak on anthropogenic influence upon a human species who existed in numbers fewer than 100,000 or 1,000,000 population when most of the temperature spike occurred. It is also ot demonstrable to find the present day temperature peak is at the end of the present integlacial period. Scientists have so far been unable to determine whether the present interglacial period ended 5,000 to 6,000 years ago, some 100,000 years in the future, or somewhere in between. Consequently, you cannot say what the maximum temperature for this interglacial period is to be with or without anthropogenic influence.

@-D. Patterson says:
March 1, 2011 at 9:27 am
“…Scientists have so far been unable to determine whether the present interglacial period ended 5,000 to 6,000 years ago, some 100,000 years in the future, or somewhere in between. Consequently, you cannot say what the maximum temperature for this interglacial period is to be with or without anthropogenic influence.”

The end of a glacial period coincides with orbital cycles that maximize seasonal solar energy in the Northern hemisphere. All previous rapid warming events from glacial to interglacial match that configuration, as does the rapid warming ~12,000 years ago.
The Eemian certainly did have a peak temperature above that seen in the present interglacial, but the Milankovitch cycles were such that the extra solar energy delivered to the N hemisphere was also greater. Note that the Eemian peak, while higher, last for a very short time and drops rapidly after it is reached.

I would agree that there is enough uncertainty in climate sensitivity to make it hard to ascribe a maximum temperature to an interglacial period from the Milankovitch cycle, but the behavior of the three previous glacial -to- interglacial transitions is clear. A rapid warming to a sharp peak that is maintained for less than 10,000 years and slower cooling to the colder glacial conditions.
This interglacial period is different in having less cooling after the peak, and present temperature at least approaching the Holocene optimum ~10,000 years ago.
Despite the Milankovitch N.H. excess having long past.

I would admit to being a little disingenuous in describing this as exceptional, there have been other interglacial transitions with less well-defined peaks, slower cooling and similar plateau states as seen at present in the temperature record. If you are willing to accept the accuracy of paleoclimate records of over half a million years ago. But if the claim is that this interglacial period is just like all the others… then the answer is it isn’t. Most show no plateau of temperature, but after a rapid rise a peak that last less than 10,000 years and a decline back to glacial conditions after the Milankovitch cycle peak has triggered the transition.

The end of a glacial period coincides with orbital cycles that maximize seasonal solar energy in the Northern hemisphere. All previous rapid warming events from glacial to interglacial match that configuration, as does the rapid warming ~12,000 years ago.

The Eemian Interglacial terminated the preceding glaciation many long thousands of years before the “orbital cycles that maximize seasonal solar energy in the Northern hemisphere” occurred. Furthermore, there is evidence of the termination of the glaciation beginning in the Southern Hemisphere and/or the Tropics before or concurrently with the Northern Hemisphere 138,000 to perhaps as far back as 140,000 years ago. In any event, the sea levels had risen most of their maximum levels, and other warming events had already been long in operation thousands of years before the astronomical orbital characteristics of the Earth resulted in the maximum insolation of the Northern Hemisphere. Your statement, “All previous rapid warming events from glacial to interglacial match that configuration, as does the rapid warming ~12,000 years ago.” are falsified by the obvious fact the glacial and interglacial periods were influenced by the Milankovitch or orbital cycles, but the inception and termination of those periods certainly do not coincide with the maximum insolation of the Northern Hemisphere.

More strikingly, the present interglacial period is not at all like the preceding three interglacial periods. Instead, the Earth’s current orbital eccentricity is at its extreme low. The last time this occurred, the interglacial period was extraordinarily longer than the other interglacials, and it was remarkably similar in temperature characteristics and timing. It is this similarity between the present interglacial and the long ago interglacial with the same orbital eccentricity which causes some researchers to conjecture the present interglacial period ending in the future up to 100,000 years from now, rather than having ended 5,000 to 6,000 years ago consistent with the most recent interglacials having more eccentric orbits for the Earth.

So even the orbital characteristics of the Earth alone render your statements false and absurd. Never mind all of the other factors besides the orbital characteristics which likely played significant roles in the inceptions of the glacial and interglacial periods a times different than the maximum solar insolation, whether or not in the Northern Hemisphere..

The Eemian certainly did have a peak temperature above that seen in the present interglacial, but the Milankovitch cycles were such that the extra solar energy delivered to the N hemisphere was also greater. Note that the Eemian peak, while higher, last for a very short time and drops rapidly after it is reached.

You have ignored the cold period in the Eemian after which the temperatures rose again to about present day levels. It appears you may be using someone’s temperature chart for something like the Antarctic ice drilling samples without understanding they are not representative in profile for the whole planet. There was a very cold period which occurred during the interglacial after which the temperatures became warm like today once more before the onset of the next glacial period.

You have also failed to see and understand how researchers have discovered some glacial periods began during an orbital period with eccentricity, obliquity, and precession of seasons that were incapable of changing the insolation of the Northern Hemisphere enough to bring about the onset of the glacial and interglacial periods. The evidence points to other factors in addition to the orbital cycles that were responsible for the glaciations and deglaciations. So your statement has no basis in fact, and it is on the contrary quite invalidated by the evidence.

I would agree that there is enough uncertainty in climate sensitivity to make it hard to ascribe a maximum temperature to an interglacial period from the Milankovitch cycle, but the behavior of the three previous glacial -to- interglacial transitions is clear. A rapid warming to a sharp peak that is maintained for less than 10,000 years and slower cooling to the colder glacial conditions.
This interglacial period is different in having less cooling after the peak, and present temperature at least approaching the Holocene optimum ~10,000 years ago.
Despite the Milankovitch N.H. excess having long past.

Your citing of “the three previous glacial -to- interglacial transitions is clear” demonstrates your failure to understand the orbital cycles and the fact that the previous three interglacials were different than the present interglacial cycle because they do not share the same eccentricity or consequent characteristics at all. On the contrary, the present interglacial period is strikingly similar to the last interglacial that had the same orbital eccentricity. Comparing this interglacial period to “the three previous glacial -to- interglacial transitions” is like comparing an elephant to three horses of different breeds. It is an invalid and, once again, absurd comparison.

I would admit to being a little disingenuous in describing this as exceptional, there have been other interglacial transitions with less well-defined peaks, slower cooling and similar plateau states as seen at present in the temperature record. If you are willing to accept the accuracy of paleoclimate records of over half a million years ago. But if the claim is that this interglacial period is just like all the others… then the answer is it isn’t. Most show no plateau of temperature, but after a rapid rise a peak that last less than 10,000 years and a decline back to glacial conditions after the Milankovitch cycle peak has triggered the transition.

To put it simply, no they don’t.

Suffice it to note, interglacial periods are relatively warmer than glacial periods, so your remark that interglacial periods are periods of natural Global Cooliing is simply misleading nonsense worthy of an Al Gore-ism.